Achieving low contact resistivity for the p-contact in silicon heterojunction (SHJ) solar cells is challenging when classic n-type transparent conductive oxides (TCOs), such as indium tin oxide (ITO), are used in the contact stack. Here, we report on SHJ solar cells with interdigitated back-contact (IBC) and a direct aluminum (Al) metallization applied to the p-contact. We find that carefully annealing an Al/a-Si:H(p) (p-type amorphous silicon) contact at moderate temperatures leads to a specific contact resistivity that is half as low as its silver (Ag)/ITO counterpart. This is explained by Al diffusing into a-Si:H(p) upon temperature treatment, forming a partially crystallized aluminum silicide layer. For a sufficiently high doping level in a-Si:H(p), this enables an efficient tunnel-recombination of holes from a-Si:H(p) to the Al contact. An estimate for this tunneling-dominated specific contact resistivity is calculated as a function of the interface doping density. Best fabricated IBC SHJ solar cells with Al p-contact yield a fill factor of 77.5% and a power conversion efficiency of 22.3%. The main differences to devices with an Ag/ITO/a-Si:H(p) contact stack are a decrease in open-circuit voltage by 14 mV and a slightly higher series resistance ( R _s ). While the first aspect can be ascribed to increased interface recombination, the second one is unexpected and requires further investigation. Interestingly, omitting an intermediate TCO does not lead to current losses in devices with Al contacts, which is further investigated by optical simulations. Finally, electrical equivalent circuit simulations are conducted to describe the electrical behavior of the investigated devices.

中文翻译：

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用于指状后接触硅异质结太阳能电池的低电阻孔接触堆栈

当在接触叠层中使用经典的 n 型透明导电氧化物 (TCO)，例如氧化铟锡 (ITO) 时，在硅异质结 (SHJ) 太阳能电池中实现 p 接触的低接触电阻率具有挑战性。在这里，我们报告了具有叉指背接触 (IBC) 和应用于 p 接触的直接铝 (Al) 金属化的 SHJ 太阳能电池。我们发现，在中等温度下仔细退火 Al/a-Si:H(p)（p 型非晶硅）触点会导致特定的接触电阻率是其银 (Ag)/ITO 对应物的一半低。这是通过 Al 在温度处理后扩散到 a-Si:H(p) 中，形成部分结晶的硅化铝层来解释的。对于 a-Si:H(p) 中足够高的掺杂水平，这可以实现从 a-Si:H(p) 到 Al 触点的空穴的有效隧道复合。这种隧道主导的特定接触电阻率的估计值被计算为界面掺杂密度的函数。最佳制造的带有 Al p 接触的 IBC SHJ 太阳能电池的填充因子为 77.5%，功率转换效率为 22.3%。与具有 Ag/ITO/a-Si:H(p) 触点堆栈的器件的主要区别是开路电压降低了 14 mV，串联电阻略高（ 电阻 _s )。虽然第一个方面可以归因于增加的界面重组，但第二个方面是出乎意料的，需要进一步研究。有趣的是，省略中间 TCO 不会导致具有 Al 触点的设备中的电流损失，这将通过光学模拟进一步研究。最后，进行电气等效电路模拟以描述所研究设备的电气行为。